Underwater explosion resistance of air-backed plate with steel and polyurea: Effect of polyurea spraying position

Abstract

Improving hull-structure resistance against underwater explosion (UNDEX) is an important problem for designers. It has been proved that polyurea coating on steel can reduce the deformation of a plate subjected to UNDEX. In this study, the effect of the polyurea position was explored by performing a series of UNDEX tests on air-backed plates. They had polyurea sprayed on the front side (PS type), back side (SP type), and both sides (PSP type). The deformation result was obtained using three-dimensional (3D) scanning technology, and the bubble movement was observed by a high-speed camera. The experimental results proved that the polyurea spraying position had no significant effect on the formation and movement of bubble or water jet. More importantly, the PS-type plate exhibited the best explosion resistance when standoff distance was less than 3Rexplosive (radius of charge), whereas the SP-type plate did so when standoff distance exceeded Rbubble (maximum bubble radius). Numerical models for these UNDEX tests were established and verified by experimental results. The numerical results demonstrated that the PS-type plate could reflect part of the energy back into the water by compression, thus reducing the energy absorbed by steel. The SP-type plate could disperse impact stress in the steel, but the protective effect was poor within close standoff distance. This was attributed to spallation under reflected tensile wave.